[Show abstract][Hide abstract] ABSTRACT: MicroRNAs are a class of naturally occurring small non-coding RNAs that target protein-coding mRNAs at the post-transcriptional level and regulate complex patterns of gene expression. Our previous studies demonstrated that in human prostate cancer the miRNA miR-125b is highly expressed, leading to a negative regulation of some tumor suppressor genes. In this study, we further extend our studies by showing that miR-125b represses the protein product of the ink4a/ARF locus, p14(ARF), in two prostate cancer cell lines, LNCaP (wild type-p53) and 22Rv1 (both wild type and mutant p53), as well as in the PC-346C prostate cancer xenograft model that lentivirally overexpressed miR-125b. Our results highlight that miR-125b modulates the p53 network by hindering the down-regulation of Mdm2, thereby affecting p53 and its target genes p21 and Puma to a degree sufficient to inhibit apoptosis. Conversely, treatment of prostate cancer cells with an inhibitor of miR-125b (anti-miR-125b) resulted in increased expression of p14(ARF), decreased level of Mdm2, and induction of apoptosis. In addition, overexpression of miR-125b in p53-deficient PC3 cells induced down-regulation of p14(ARF), which leads to increased cell proliferation through a p53-independent manner. Thus, we conclude that miR-125b acts as an oncogene which regulates p14(ARF)/Mdm2 signaling, stimulating proliferation of prostate cancer cells through a p53-dependent or p53-independent function. This reinforces our belief that miR-125b has potential as a therapeutic target for the management of patients with metastatic prostate cancer.
PLoS ONE 01/2013; 8(4):e61064. · 3.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Patients with recurrent prostate cancer are commonly treated with androgen withdrawal therapy (AWT); however, almost all patients eventually progress to castration resistant prostate cancer (CRPC), indicating failure of AWT to eliminate androgen-sensitive prostate cancer. The overall goal of these studies is to determine whether dual inhibition of the receptor tyrosine kinases epidermal growth factor receptor (EGFR) and HER2 would prolong the effectiveness of this treatment in prostate cancer.
We used androgen-dependent LNCaP cells and its CRPC sublines LNCaP-AI and C4-2. Additional data were collected in pRNS-1-1 cells stably expressing a mutant androgen receptor (AR-T877A), and in nude mice harboring CWR22 tumors. Studies utilized EGFR inhibitors erlotinib and AG1478, and HER2 inhibitors trastuzumab and AG879.
Dual EGFR/HER2 inhibition induced apoptosis selectively in androgen-sensitive prostate cancer cells undergoing AWT, but not in the presence of androgens, or in CRPC cells. We show that AWT alone failed to induce significant apoptosis in androgen-dependent cells, due to AWT-induced increase in HER2 and ErbB3, which promoted survival by increasing Akt phosphorylation. AWT-induced ErbB3 stabilized the AR and stimulated PSA, while it was inactivated only by inhibition of both its dimerization partners EGFR and HER2 (prostate cancer cells do not express ErbB4); but not the inhibition of any one receptor alone, explaining the success of dual EGFR/HER2 inhibition in sensitizing androgen-dependent cells to AWT. The effectiveness of the inhibitors in suppressing growth correlated with its ability to prevent Akt phosphorylation.
These studies indicate that dual EGFR/HER2 inhibition, administered together with AWT, sensitize prostate cancer cells to apoptosis during AWT.
Clinical Cancer Research 08/2011; 17(19):6218-28. · 7.84 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The androgen receptor (AR) acting as a transcription factor plays a pivotal role in the occurrence and progression of prostate cancer (CaP). Several AR-related factors or modulators have been reported to influence AR activity. Whether and how these factors cooperatively modulate the AR activity has not been well defined. In the present study, the combined effect of p160 coactivators, short CAG length (encoding a short polyQ tract), and AR mutations on AR transactivation in a yeast system was evaluated. It was found that the short polyQ tract can upregulate the transactivation of the wild-type (WT) AR and partial-function (PF) AR mutants in response to a physiological level (10(-9) M) of dihydrotestosterone. Addition of a p160 coactivator (SRC-1 or TIF2) to the above systems resulted in a significant increase in the ligand-stimulated transactivation. Although the androgen antagonist bicalutamide could suppress the activity of androgen-activated WT or PF ARs, it was unable to do so for gain-of-function AR mutants. A combination of the short polyQ tract and coactivator TIF2 acted cooperatively on the WT AR and PF AR mutants to enhance their transactivation in response to either a low level of dihydrotestosterone (10(-10) M) or adrenal dehydroepiandrosterone. Taken together, this finding suggests that the modulated AR activity may involve early in the carcinogenesis of CaP. Additionally, these data support the concept that a given CaP in which the AR activity is modulated by multiple AR modulators may progress more readily to castrate resistance.
Cancer Biotherapy & Radiopharmaceuticals 04/2011; 26(2):191-201. · 1.44 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Increasing evidence demonstrates that aberrantly regulated microRNAs (miRNAs) contribute to the initiation and progression of human cancer. We previously have demonstrated that miR-125b stimulated the growth of prostate cancer (CaP) cells. In this study, we further determined the influence of miR-125b on the pathogenesis of CaP.
To evaluate the effect of miR-125b on xenograft tumor growth, male athymic mice were subcutaneously injected with PC-346C-miR-125b cells that stably overexpressed miR-125b. Potential direct target transcripts of miR-125b were identified using a bioinformatics approach and three miR-125b targeted molecules were confirmed by means of biochemical analyses.
Enforced expression of miR-125b promoted tumor growth in both intact and castrated male nude mice. In an effort to define the molecular mechanism(s) mediating its tumor growth properties, we found that miR-125b directly targets eight transcripts, including three key pro-apoptotic genes: p53, Puma, and Bak1. Increasing the abundance of miR-125b resulted in a dramatic decrease in the levels of these three proteins in CaP cells. A direct repressive effect on each of these was supported by the ability of miR-125b to significantly reduce the activity of luciferase reporters containing their 3'-untranslated regions of each gene encompassing the miR-125b-binding sites. Additionally, we found that repression of miR-125b activity was able to sensitize CaP cells to different therapeutic interventions.
Data obtained in this study demonstrate that miR-125b promotes growth of prostatic xenograft tumors by down-regulating three key pro-apoptotic genes. This suggests that miR-125b is oncogenic and makes it an attractive therapeutic target in CaP.
The Prostate 09/2010; 71(5):538-49. · 3.84 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Growth of most ablation-resistant prostate cancers (CaPs) is dependent on androgen receptor (AR) activity in chromatin, but cancer cells in these tumors have acquired altered AR activation. It is unclear how the aberrantly activated AR loads onto regulatory regions of AR-targeted genes. The purpose of this study was to assess the AR chromatin loading in an androgen-depleted environment.
The expression of PSA in androgen-resistant CaP cells was determined using RT-PCR and Western blot analysis. In order to investigate the binding of the AR to the PSA gene regulatory regions, chromatin immunoprecipitation (ChIP) was performed in the androgen-independent cds2 cell line in the presence or absence of androgens. In addition, we examined the involvement of p160 coactivators in the chromatin loading of the AR.
It was found that constitutive activation of PSA expression was the result of sustained occupancy by the AR at the regulatory region of this gene. This stable AR loading was not blocked by the AR antagonist bicalutamide. Furthermore, androgen-resistant CaP cells highly expressed both AR and the p160 coactivators and the AR was able to recruit TIF2. Downregulation of TIF2 using short hairpin RNA disrupted the AR loading to the PSA enhancer and subsequently inhibited AR activity.
Prolonged AR localization to the regulatory regions of AR targeted genes and the recruitment of p160 coactivators are a potential mechanism leading to androgen-independent activation of the AR. Disruption of AR chromatin loading could therefore become an important therapeutic target for this disease.
The Prostate 10/2008; 68(16):1816-26. · 3.84 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Although prostate cancer (CaP) is the most frequently diagnosed malignant tumor and the second leading cause of cancer deaths in American men, the mechanisms explaining the development and progression of CaP remain largely unknown. Recent studies have shown that some aberrantly expressed microRNAs (miRNAs) are involved in tumorigenesis. Although aberrant expression of certain miRNAs has been discovered in CaP, their function in this disease has not yet been defined. In this study, we found differential expression of miR-125b in androgen-dependent and independent CaP cells, as well as in benign and malignant prostate tissues. Furthermore, androgen signaling was able to up-regulate the expression of miR-125b. In addition, transfection of synthetic miR-125b stimulated androgen-independent growth of CaP cells and down-regulated the expression of Bak1. Our results suggest that miR-125b acts as an oncogene, contributing to the pathogenesis of CaP.
Proceedings of the National Academy of Sciences 01/2008; 104(50):19983-8. · 9.81 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The role of androgen receptor (AR) mutations in the initiation of prostate cancer (CaP) remains unclear. The purpose of this study was to assess the influence of an AR mutation on prostate tumorigenesis and to determine the resulting molecular alterations.
Wild-type AR (AR(WT)) or the CaP-derived K580R AR (AR(K580R)) mutant was stably transfected into SV40-immortalized human prostate epithelial pRNS-1-1 cells that lack AR expression and fail to grow in nude mice. The ability of these AR-transfected cell lines to form tumor was investigated in vitro and in vivo. Additionally, gene expression profiling of these cell lines was performed.
Compared with the AR(WT), the AR(K580R) induced greater than sixfold increase in colony formation in soft agar. In vivo studies confirmed that the AR(K580R)-transfected pRNS-1-1 cells were able to form tumors in nude mice. Using a combination of microarray and RT-PCR, 29 differentially expressed genes were identified in AR(K580R) cells. It was found that silencing the expression of placental alkaline phosphatase (ALPP) that was upregulated in AR(K580R) cells resulted in significant inhibition of cell growth. Furthermore, the AR(K580R)-transfected pRNS-1-1 cells expressed markedly increased p-Akt and p-p70 S6K.
The AR(K580R) mutation promoted the malignant transformation of prostate epithelial cells. This was associated with upregulation of ALPP and subsequent activation of the Akt signaling pathway.
The Prostate 06/2007; 67(6):591-602. · 3.84 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Genistein combined polysaccharide (GCP) is a nutritional supplement that can inhibit prostate cancer growth experimentally and clinically. It is composed predominantly of the isoflavones genistein, daidzein, and glycitein, which have anti-cancer properties. Although genistein is well studied, the properties of GCP are not well defined. The goal of this work was to better characterize the signaling pathways impacted by GCP in an effort to optimize its efficacy.
Cell growth and apoptosis were evaluated by MTS proliferation, caspase-based assays, and flow cytometry. Modulation of androgen receptor (AR) levels and activation status of signaling molecules were monitored by immunoblot analysis. AR function was measured by evaluating prostate-specific antigen (PSA) message and protein levels and by reporter assays.
GCP inhibited proliferation of androgen-dependent LNCaP and androgen-independent LNCaP-p53(GOF) and 22Rv1 cell lines in a dose-dependent manner and cells were more responsive in the presence of androgen. GCP markedly suppressed mTOR-p70S6K signaling while Akt and p53 were only modestly modulated. GCP significantly attenuated androgen signaling as evidenced by diminished AR protein levels and a consequent reduction in transcriptional activity and PSA expression. AR expression was enhanced by de-repression of translation with inhibitors of PI3K-Akt-mTOR signaling and by inhibition of proteasome-dependent degradation. Neither inhibitor could counteract GCP-mediated AR downregulation, suggesting the involvement of a mechanism(s) independent of these pathways.
Our results suggest that GCP mediates growth inhibition and apoptosis through multiple mechanisms including (1) molecular mimicry of androgen ablation (via AR downregulation) and (2) by providing an AR-independent, pro-apoptotic signal (mTOR inhibition).
The Prostate 05/2007; 67(5):521-35. · 3.84 Impact Factor